Ultrasound scan

Page last reviewed: 13/07/2011

An ultrasound scan, sometimes called a sonogram, is a procedure that uses high frequency sound waves to create an image of part of the inside of the body, such as the heart. As sound waves are used rather than radiation, the procedure is believed to be completely safe. Ultrasound scans are commonly used during pregnancy to produce images of the baby in the womb.

Ultrasound waves are directed at your body using a small handheld sensor called a transducer. This is moved over the surface of the skin and generates sound waves. When the sound waves hit an object, such as a heart valve, they bounce back as an echo. A computer converts the reflected ultrasound echoes into an image.

Ultrasound scans can be used to help doctors make a diagnosis or to assess the effects of a treatment. They can also be used to study blood flow and to detect any narrowing or blocking of blood vessels.

Internal examinations

There are different kinds of ultrasound scans depending on what part of the body is being scanned and why. Occasionally doctors need to do examinations that involve an ultrasound probe being placed into the vagina or rectum to look more closely at internal structures. Internal examinations may cause some discomfort but ultrasound scans do not usually cause any pain.

Page last reviewed: 13/07/2011

Monitoring an unborn baby

An ultrasound scan is a routine procedure for pregnant women. It produces an image of the unborn baby inside the womb, and displays it on a monitor.

Most women are offered at least two ultrasound scans during pregnancy:

  • the first scan (at around eight to 14 weeks) can help to determine when the baby is due, and
  • the second scan (usually between 18 and 20 weeks) checks for structural abnormalities, particularly in the baby's head or spine.

Detecting heart problems

An ultrasound scan can be used to examine the size, shape and movement of your heart. For example, it can check that the structures of your heart, such as the valves and heart chambers, are working properly and your blood is flowing normally. This type of ultrasound scan is called an echocardiogram.

Echocardiograms can also be used to diagnose heart problems in babies, even before they are born. This is called foetal echocardiography, and it is carried out during routine antenatal examinations.

For more information, see Diagnosing congenital heart disease.

Examining other parts of your body

Ultrasound can help diagnose problems in your:

  • liver,
  • gallbladder,
  • pancreas,
  • thyroid gland,
  • lymph nodes,
  • ovaries,
  • testes,
  • kidneys,
  • bladder,
  • breasts,
  • blood vessels,
  • joints, ligaments and tendons,
  • skin,
  • eyes, and
  • the brain and spine in newborns.

It can detect gallstones, tumours, fluid-filled cysts and any narrowing or swelling of blood vessels.

Surgical procedures

Ultrasound can be used to guide doctors during surgical procedures, such as biopsies (where a tissue sample is taken for analysis), to make sure they are working in the right area.

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The limitations of ultrasound

Ultrasound waves cannot pass through bone, air or gas. This means they are unable to produce clear and detailed images of some parts of the body, such as the brain, because it is surrounded by bone.

Other scanning methods, such as barium tests, CT scans and magnetic resonance imaging (MRI) scans can be used to examine parts of your body not suitable for ultrasound scanning.

Page last reviewed: 13/07/2011

Before having an ultrasound scan, you may be asked to prepare for the procedure. For example, before you have a foetal (baby) scan, or a scan of an organ in your pelvic area, you may be asked to fill your bladder by drinking water and not passing urine until after the test.

For other procedures, such as scans of the gallbladder or pancreas, you may be asked not to eat or drink for up to four hours before the test.

The scan

There are three main types of ultrasound scan:

  • external ultrasound,
  • internal ultrasound, and
  • endoscopic ultrasound

External ultrasound

An external ultrasound scan is commonly used to examine your heart or an unborn baby in your womb. A small hand-held device called a transducer is placed onto your skin, and moved over the part of the body that will be examined.

A lubricating gel is put onto your skin that allows the transducer to move smoothly and ensures there is continuous contact between the sensor and the skin. The transducer is connected to a computer and a monitor. Pulses of ultrasound are sent from a probe in the transducer, through your skin and into your body. Ultrasound waves are bounced back from the structures of your body and are displayed as an image on the monitor.

As well as producing still pictures, an ultrasound scan shows movement that can be recorded onto video.

The external scan is painless. You should not feel anything other than the sensor and gel on your skin (which is often cold). If you are having a scan of your uterus, your full bladder may cause you some discomfort. The whole procedure usually takes from 15 to 45 minutes.

Internal ultrasound

Occasionally doctors need to do internal examinations to look more closely at structures such as the prostate gland or womb. This involves an ultrasound probe being placed into the vagina or rectum. Internal examinations may cause some discomfort but do not usually cause any pain.

Endoscopic ultrasound

Endoscopic ultrasound is where a long, thin, flexible tube (endoscope) is inserted into your body, usually through your mouth, to examine areas such as your stomach, food pipe (oesophagus) and small bowel (duodenum).

The endoscope has a light and an ultrasound device on the end. Once it has been inserted into the body, ultrasound waves are used to create images in the same way as an external ultrasound.

Endoscopic ultrasound can be uncomfortable and may make you feel sick. You will usually be given painkillers and a sedative to keep you calm.

Internal and endoscopic ultrasound is more effective than external ultrasound for examining some organs in close detail. However, because an object enters your body, there is more discomfort and a small risk of side effects, such as internal bleeding.


The bladder is a small organ near the pelvis that holds urine until it is ready to be passed from the body.
A foetus is an unborn baby, from the eighth week of pregnancy until birth.
The uterus (also known as the womb) is a hollow, pear-shaped organ in a woman where a baby grows during pregnancy.
The heart is a muscular organ that pumps blood around the body. 
The anus is the opening at the end of the digestive system where solid waste leaves the body.

Who will perform your ultrasound scan?

Your ultrasound scan will generally take place in an X-ray department in hospital and be performed either by a doctor, who will provide a diagnostic report, or by a sonographer. A sonographer a specialist trained in the use of ultrasound, who will provide a descriptive report for the doctor to make a diagnosis.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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